[ http://www.wired.co.uk/news/archive/2014-07/23/happy-batman-day ]
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DC Comics has declared 23 July to be this newest and most sacred of holidays, celebrating the debut of the Caped Crusader in the pages of Detective Comics #27. However, that issue is cover dated May 1939, and due to the tendency for periodicals to be future-dated (back in the news stand era, it helped older issues stay looking current) may have been on sale as early as March. Oops. As far as actual Bat-anniversaries that might be celebrated this month, the July 1939 cover dated issue 29 has the first appearance of the iconic utility belt and the villain Doctor Death. The September 1939 dated issue 31, which would have been sold in July, features the first use of the Batarang weapon and the Batgyro, the first of Batman's expanded fleet of vehicles.
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